Electrical resistor



Oct. 14, 1958 H. FRUTH ELECTRICAL RESISTOR Filed Nov. 15, 1954 flzfi ATTORNEYS I N VEN TOR.

United States Patent ELECTRICAL RESISTOR Hal F. Fruth, Skokie, Ill.

Application November 15, 1954, Serial No. 468,698

Claims. (Cl. 201-63) This invention relates to electrical resistors and more particularly to wire type precision resistors.

In wire type resistors it has been a problem to minimize the induction and capacity effects while at the same time accurately maintaining the desired resistance values. The problem of handling the wire in manufacture to maintain uniformity among a number of resistors and to minimize cost has also been an extremely diflicult one.

It is therefore one of the objects of the present inven tion to provide an electrical resistor which is easy and inexpensive to manufacture with a high degree ofuniformity and in which the induction and capacity effects are minimized.

Another object is to provide a resistor in which the wire is formed into a series of fiat loops having substantially straight parallel sides.

According to one feature of the invention, the loops are connected together to form a flat tape which may be rolled into a cylinder to fit into a tubular insulating body. In one form, the loops are secured together by a film of non-conducting adhesive and in another form, the loops are formed by stitching the wire in zig-zag stitches to a flat flexible tape. As an alternative to rolling the tape, the loops may simply be pressed together to form an elongated body with the loops lying in side-by-side relationship.

A further object is to provide a resistor in which the ends of the wire extend from the ends of the rolled or pressed body through the ends of the mounting tube and are engaged by terminals pressed into the ends of the tube to establish an electrical connection to the resistor.

The above and other objects and features of the invention will be more readily apparent from the following description when read in connection with the accompanying drawings, in which:

Figure 1 is a side elevation with parts in section of an insulator embodying the invention;

Figure 2 is an enlarged transverse section taken centrally of the length of Figure 1;

Figure 3 is an elevation of a flat resistor tape formed according to the invention;

Figure 4 is a perspective view showing the tape rolled up for mounting in an insulating tube;

Figure 5 is a partial enlarged elevation of the resistor of Figure 3;

Figure 6 is a partial section on the line 6-6 of Figure 5;

Figure 7 is an elevation of an alternative form of resistor element;

Figure 8 is a top plan view of an apparatus for forming a resistor element according to a further alternative; and

Figure 9 is a side elevation of the apparatus of Figure 8.

A completed resistor, according to the present invention, is illustrated in Figures 1 and 2 and may comprise a tube 10 of insulating material, such as a ceramic, a relatively hard plastic, or the like. The tube is adapted to receive a resistor element, indicated generally at 11,

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formed of an elongated resistance wire, as described more particularly hereinafter. The resistor element includes wire ends, shown at 12, extending through the open ends of the tube 10 for connection to terminals.

As shown in Figure 1, the wire ends 12 may be stripped and may be engaged by enlarged end portions 13 on elongated Wire terminals 14. The terminals 14 may be a relatively heavy wire through which the resistor is connected into a circuit and the enlarged end portions 13 may be formed on the wire in the manner more particularly described and claimed in my co-pending application, case No. 54,047. When the end portions 13 are forced into the ends of the tube 10 they will function both to close and seal the ends of the tube and to establish electrical contact with the wire ends 12. After assembly of the parts, the entire insulator may be dipped in wax or varnish, or the like, for sealing purposes, if desired.

The resistor element is formed, according to the present invention, of an elongated wire shaped into a series of flat loops having substantially straight parallel sides. As shown in Figures 3 to 6, a wire 15, preferably a very fine wire of high resistance material, is looped back and forth upon itself to define a series of interconnected loops having straight sides 16 joined by semi-circular re-bends 17 at the ends of the loops. The wire may be formed continuously in this manner and cut off to any desired length to provide the desired resistance value.

With a wire so formed, a very low inductance is produced due to the fact that the wire consists principally or a series of straight parallel runs through which current flows in opposite directions. Also because the runs of wire constituting the sides of the loops are spaced apart, the capacity effect is minimized. The completed unit therefore provides substantially pure resistance with a minimum inductance and minimum capacity.

The loops of wire are preferably secured together for easy handling in the form of a flat tape. In the embodiment of Figures 3 to 6, this is accomplished by coating or embedding the wire in a non-conducting adhesive film 18 of wax, varnish, plastic, or the like. As best seen in Figures 5 and 6, the adhesive film holds the lengths of wire together in the form of a flat tape which can easily be handled and in which the wire is uniformly spaced throughout the several loops. The length of tape may be cut off as desired to provide the desired resistance value with the ends projecting therefrom and scraped. The tape may then be rolled upon itself, as shown in Figure 4, to provide a substantially cylindrical form of a size to be inserted in a tube 10.

An alternative method of forming the resistor element is illustrated in Figure 7 wherein a flat tape 19 of insulating material is provided and the wire, as shown at 21, is stitched thereto in the form of a series of zig-zag stitches. The tape 19 may be formed of any desired nonconducting material which will withstand the temperatures developed in operation of the resistor such, for example, as a thin woven glass fiber tape, asbestos tape, or the like. The stitches may be formed by a conventional type of sewing machine utilizing the wire itself for one of the threads and a fibrous non-conducting thread for the other. After the wire has been stitched to the tape, the necessary length to provide the desired resistance may be cut off and rolled, as indicated in Figure 4, for insertion in an insulating tube, such as the tube 10.

Instead of forming the wire into a tape, the wire may be wound into a series of loops ona rotary winding head which are simply pressed together to form the resistance element. Figures 8 and 9 illustrate a head for winding the wire consisting of a rotatable body 22 having a series of spaced pins 23 at its periphery and a corresponding a se1 '-ie's--ofpins"24 adjacentits center. A wire, as shown at 25, preferablypre-coated with insulation, is wound alternately around inner and outer pins to provide a series of substantially radially extending loops on the head. The loops may be secured byanadhesive, such-as wax,"varnish, orthe like, -before*being removed from thehead or may simply be' lifted*frorn the pins23 and 24 and bunched together with the sides ofthe loops lying generally parallel to'each 'other. Theelongated bodyso'formed-may be inserted in an'insulatingtube'with the endsof the wire projecting'for connection to terminals, as -shown-in Figure 1.

In all embodiments, the resistor element is defined "by a wireformed into a series of fiat loopswhich are pressed or'rolled together -to form a compact body which maybe mounted "in an insulating tube.- In all-cases; inductance is minimized by the-fact that the-wire is in the --form of straight -sided'=loops'=throughwhich current flows in opposite directions and" capacity is minimized by the fact that rthe wires are spaced apart in'the final element. The wire can alson-be handled easily and almost entirely with automatic machinery since the wires once woundto-the desired formmaybe-seeured in position by' an adhesive film orbya preformed tape element.

While several embodiments of the-inventionhavebeen shown-and described herein, it will be'understood'that they are illustrativeonly and notto be-taken as a definitiontofgthe scope oftheinvention, reference being had for this purpose to. the:appended..clairns..

Whatiis claimed-is:

. I. .An electrical resistor. comprising: an-elongated .wire formed into a series 10f flat-loops:havingsubstantially straight parallel-sides joined :by .re-bent portions,- and a non-conducting adhesivamaterialcovering the wire and forming arfilm between adjacent sides of the loops to join the :loops in the;form.rofia flat.,tape.:and...the tape being rolled into .-a cylindrica1;body with.;the;sides of the loops extending. axiallysof ,the. body.

2..,An.- electrical resistor; comprising an: elongated .flat tape of non-conducting;material,. and.an; elongated wire formed; into aseries of flat .loops .having substantially straight parallel sides joinedby-rebent portions, .the :re-

v 5.2 bent portions being'stitched through the tape to secure the wire thereto.

3. An electrical resistor comprising an elongated flat tape of non-conducting material, and an elongated wire formed into a series of flat loops having substantially straight parallel sides joined by rebent portions, the rebent portions being stitched through the tape to secure the wire thereto, the tape being rolled into a substantially cylindrical form withnthe sides of the loops extending axially of the formand-the ends ofthe 'wire extending from the cylindrical form for connection to terminals.

4. An electrical resistor comprising a tubular insulating housing, an elongated wire -'fo1'med*into"a-Series otfiat loops each having substantially straight parallel sides joined by re-bent portions, the loops being formed into an elongated compact body with the sides of the loops extending lengthwise of the body and fitting in the tube with the ends of the wire projecting through the ends of the tube, and terminals having'end portions fitting in-the ends of the tube and'engaging the-ends of the wire to establish electrical 'contactLtherewith:

5. An electrical resistor=cornprisingatubular-"insulatinghousing, an elongated wirefo'rmedintoa series of flat loops each having substantially straight parallel: sides joined by re-bent portions,- insulating means connectingthe loops in the form of afiat tape,--the tape being rolled upon itself into =a-substantiallyvcylindrical body fitting in the tube with the ends of the wire extending'from the ends of the body out the ends of the tube,- and' terminals having end portions fitting-in the: ends 1 of the -tube= and engaging the ends of the wire to establish electrical contact there with.

References Cited in the :filerofthisg-patent' UNITED STATES PATENTS 2,360,267 Osterheld Oct. 10, 19.44 2,387,995 Huck .,Oct..30, .1945 2,548,592 Michele ,Apr.,,l0, 1951 2,559,077 Johnson .etaL. 'lulyf3, .1951 2,582,341 Levers et a1 ,f-Jan. 15,, 1952 2,637,766 Grouse fMay 5, 1953 

